Partial-cutting machines have been provided heretofore for advancing a tunnel, gallery, drift or other mining or subsurface passage through a subterranean structure by progressively cutting away the face of this structure in the direction in which the tunnel is to be advanced.
The equipment utilized for this purpose can include a cutting head formed with milling teeth and rotatable to bite into the face of the subterranean structure.
Such tunneling apparatus can include a vehicular structure upon which the milling head is carried and which is movable along the floor of the tunnel or gallery, e.g. via crawler treads, a turntable on the vehicle body, an outrigger arm or boom extending from the turntable and swingable thereby, and the cutting head at the end of this boom. The vehicle structure also carries a prime mover and various hydraulic or other apparatus for the movements which are to be effected and the control system.
Such machines may be operated by personnel on or alongside the machine or even by remote control
More specifically, the tread or crawler chassis may be displaced by a hydraulic motor driven by a pump connected to the prime mover or by some other transmission interposed between the prime mover and the tread of the tracked vehicle, hydraulic piston-and-cylinder arrangements (hydraulic jacks) may be provided to swing the boom or arm upwardly or downwardly about a horizontal axis, a rotary hydraulic motor also energized by the pump can be provided to drive the turntable to allow swinging of the arm from side to side, and similar hydraulic means can be provided to extend and retract the boom or arm.
The cutting head at the end of the arm may be provided with its own drive, e.g. a hydraulic or electric drive.
In general, such machines have operated in the past to advance a mine tunnel by sinking the head into the tunnel face to a predetermined depth and then swinging the head to one side and/or the other and thereby mill away the subterranean structure beneath an overlying body and above an underlying body. When the cut has been completed over the width of the mine tunnel, the head is moved upwardly or downwardly into the overlying body or the underlying body and the swinging movement is repeated. This process is repeated until the entire face has been cut away by such partial cuts to the aforementioned predetermined depth.
It is useful to define, for the purpose of this disclosure, an "increment" of attack, also referred to as the "attack increment", to mean the area over which the cutting head attacks the structure as it is swung to one side or the other in excavating horizontal cuts in the manner described. This attack increment is, of course, increased by increasing the penetration of the cutting head into the face and will generally be related to the height of the cut and/or to the product of the height and the depth of the cut.
Generally speaking in the earlier systems, once penetration was accomplished to the desired depth, the attack increment was the same for the initial cut and for the cuts thereabove and below until the entire face was excavated to the aforementioned predetermined depth.
During the excavation, the swing moment of the arm can vary and, of course, depended upon the resistance of the structure to the cutting action of the head and to its lateral movement in advancing the cut and thus to the force applied to the arm through the turntable, tending to swing the arm and laterally displace the head.
After the face had been competely cleared, a new penetration was made and the process repeated, thereby advancing the tunnel, gallery or drift by a series of partial cuts. The cutting head itself can have the configuration of a disk such that the depth of penetration corresponded to the thickness of the disk and the disk was oriented orthogonally to the direction of advance, the disks cutting strips whose thickness has defined the attack increment. The cutting head also may be a ball or cone shaped member or even a cylindrical body formed with spherical or helical arrays of teeth.
The penetrataion depth and the attack increment are, of course, selected in dependence upon the type of structure which is encountered, namely, the hardness or softness of the rock strata and other characteristics thereof and determine in turn, the volume rate of flow of the recovered rock i.e. the amount of rock removed from the face per unit time.
In utilizing the aforedescribed technique and machines, the depth of penetration and the attack increment are generally predetermined, based upon observation by the operator, test data from sampling or the like of the hardness of the rock structure or other empirical matters.
Utilizing predetermined and precalculated parameters of this type, however, it is not always possible to optimize the rate of removal of the rock structure. It is difficult, if not impossible, to optimize the cutting efficiency and it is not always possible for the operator to respond sufficiently rapidly to undue stress upon the machine parts or to prevent such undue stresses from reaching critical values or even damaging the apparatus.